Road Test: Mercedes-Benz E Class E250 CDI BlueEFFICIENCY SE 2dr Tip Auto

Alright, so it's a diesel cabrio. We could slag it off for dirtying the roofless driving experience, and insist that it really should have a growly petrol engine to make your dangly bits buzz. But we'd be wrong. Diesel cabs are a solid part of our world now, and besides, the Mercedes E-Class cab is a softie cruiser that doesn't need thrashing. So diesel it is. Fine.

But a manual gearbox? That's weird. When we first drove this thing last month, we tried the 7G-Tronic auto in the petrol version, which suited the car perfectly. It shifts rapidly enough when needed, then relaxes into recline and-waft mode once the quick bits are over. By contrast, this manual feels elastic and each gear is selected with a rubbery twang rather than a satisfying snick.

And who wants to waste time changing gear? A serene machine like this should do the work for you. Our manual test car eased the load slightly with a hill-hold function, but that's essential, as Merc handbrakes are actually footbrakes, so to perform a hill start you'd need to sprout an extra leg to work brake and clutch simultaneously.

Admittedly, the manual will save you a few grams of CO2 over the 7G shifter, and the auto is a £1,490 option. But consider this: on average you change gear 96,000 times in 10,000 miles. That works out at around 1.5p per shift, for a whole year's motoring. Over the car's lifetime it's something like 0.0001p per shift. So well worth the investment in other words, and given the price of the car, hardly a fortune.

But enough about that. The irritating manual distracts from a very good engine. It might only be a four-cylinder diesel, but it's about as good as four-cylinder diesels get. You could be fooled into thinking it's bigger, especially by the smooth, quick and quiet way it delivers its 204bhp and 368lb ft of torque. And not many 2.1-litre diesels need electronic restraint at 155mph. It's clean too, thanks to Blue Efficiency boffinry that helps the 250CDI to a claimed 50.4mpg on the combined cycle.

We're big fans of the Mercedes E-cab. It's a classy car that should be driven elegantly. So forget the sticky manual and spend extra on the auto (historically, 97 per cent of E-Class buyers do, according to Mercedes). And don't be shy of this diesel. Ten years ago that advice would deserve flagellation... but the world has changed. Perhaps a light spank will do for now.